如何用JavaScript按metadata.id合并对象并实现tests属性求和？

输入数据 #

let input = {
  "data": [
    {"state": "CA","tests": 12,"city": [ "Mountain View"],"metadata": { "id": 15 }},
    {"state": "TX","tests": 10,"city": [ "Austin" ],"metadata": { "id": 15 }},
    {"state": "AZ","tests": 5,"city": [ "Flagstaff" ],"metadata": { "id": 10 }}
  ]
}

合并需求 #

将metadata.id相同的对象合并：

• state和city属性拼接为数组（单个元素时state用字符串，多个元素时保留数组）
• tests属性求和
• metadata保留原对象

预期输出 #

let result = {
  "data": [
    {"state": ["CA", "TX"],"tests": 22,"city": ["Mountain View", "Austin"],"metadata": { "id": 15 }},
    {"state": "AZ","tests": 5,"city": [ "Flagstaff" ],"metadata": { "id": 10 }}
  ]
}

我的尝试代码 #

我用reduce实现时，无法正确完成tests属性累加，代码如下：

let total_tests = 0;
let res = [{
  data: Object.values(input[0].data.reduce((acc, {state, city, metadata, tests, category}) => {
    const id = metadata?.id;
    if (!acc[id]) {
      acc[id] = {id,state: [],city: [],metadata,tests,category}
    }
    acc[id].state.push(state)
    acc[id].city.push(...city)
    acc[id].tests = total_tests + acc[id].tests;
    return acc
  }, {}))
}]

正确实现方案 #

问题出在使用全局变量total_tests累加，导致所有id的tests共用同一个值，且初始化时直接赋值当前对象的tests，未做累加逻辑。修正后的代码如下：

const result = {
  data: Object.values(input.data.reduce((acc, item) => {
    const id = item.metadata.id;
    // 初始化当前id的合并对象
    if (!acc[id]) {
      acc[id] = {
        state: [],
        city: [],
        tests: 0,
        metadata: item.metadata
      };
    }
    // 累加tests
    acc[id].tests += item.tests;
    // 收集state
    acc[id].state.push(item.state);
    // 展开city数组添加
    acc[id].city.push(...item.city);
    
    return acc;
  }, {})).map(mergedItem => {
    // 单个state转为字符串，匹配预期输出格式
    mergedItem.state = mergedItem.state.length === 1 ? mergedItem.state[0] : mergedItem.state;
    return mergedItem;
  })
};

核心修正说明： #

1. 移除全局变量total_tests，每个id的tests单独维护，初始设为0，每次循环累加当前项的tests
2. 修正原代码中input[0].data的错误，直接取input.data
3. 通过map处理state格式，单个元素转为字符串，多个元素保留数组
4. 移除原代码中未用到的category属性，避免冗余

内容的提问来源于stack exchange，提问作者Aren Trot